Speaker
Description
Non-destructive testing (NDT) techniques are essential for evaluating the integrity, reliability, and safety of engineering components without impairing their serviceability. NDT methods are widely employed in critical industrial sectors such as power generation, aerospace, manufacturing, and infrastructure, where early detection of defects can prevent catastrophic failure and reduce maintenance costs. Among the various NDT techniques, thermal-based methods have gained increasing importance due to their capability to detect surface and subsurface anomalies in a rapid, full-field, and non-contact manner.
Infrared thermography is a well-established thermal NDT technique that enables spatial and temporal measurement of temperature variations associated with material inhomogeneities and defects. In conventional active infrared thermography, external thermal excitation is applied to a specimen, and the resulting transient thermal response is monitored using an infrared camera. Defects such as voids, cracks, and inclusions disturb heat flow within the material, producing detectable thermal contrasts on the surface. The effectiveness of this technique strongly depends on the characteristics of the thermal excitation source, including its intensity, duration, uniformity, and spectral properties.
While extensive research has focused on optimising excitation power, heating time, and post-processing algorithms, the influence of excitation source colour temperature on defect detection has received limited attention. In this study, an experimental investigation is conducted to evaluate the effect of colour temperature on defect detectability in mild steel using an active infrared thermographic technique. LED-based lamps with adjustable colour temperature capability are employed as the thermal excitation source due to their stability, energy efficiency, and spectral controllability.
The colour temperature of the LED lamps is systematically varied over a predefined range, while all other experimental parameters, such as excitation power, heating duration, infrared camera settings, inspection geometry, surface condition, and ambient environment, are maintained constant. This controlled approach enables the isolation of the colour temperature effect on the specimen's thermal response. A mild steel sample containing artificially induced defects of known geometry and depth is used to ensure repeatability and objective comparison.
Thermal data are acquired during both heating and cooling phases using a calibrated infrared camera. The recorded thermograms are analysed with a primary focus on the signal-to-noise ratio (SNR), which serves as the quantitative metric for comparing defect detectability across different colour temperature conditions. SNR values are calculated by comparing the thermal responses of defective regions with those of sound areas. The experimental results reveal that colour temperature significantly influences thermal contrast generation and defect visibility, with certain colour temperature settings yielding higher SNR values and improved defect discrimination.
The findings demonstrate that optimising colour temperature can enhance defect detection performance in conventional infrared thermographic NDT without increasing excitation energy, inspection time, or system complexity. This study highlights colour temperature as a critical yet often overlooked parameter and provides practical guidance for improving thermographic inspection sensitivity. The outcomes contribute to quantitative infrared thermography research and support the development of more efficient and adaptable NDT systems for metallic components.
